I. Field of the Invention
The invention relates to a sealer for asphalt pavement or metal surfaces.
II Description of the Prior Art
There are two basic types of driveway or pavement sealerxe2x80x94coal tar based and asphalt based. These materials are primarily used to seal driveways and other pavement surfaces, but can also be used to seal metal surfaces, e.g., pipe coatings.
Coal tar is the premier product and has the largest market share. Driveway sealer made from coal tar is an emulsion of water, coal tar pitch, clay and water, perhaps with emulsifier and optional ingredients such as sand. These materials are long lasting, have a pleasing black color and are resistant to gasoline and kerosene spills, but have an objectionable odor during application and contain aromatic compounds, some of which are polynuclear aromatics (PAHs). Economic costs for coal tar derived products are higher than petroleum. Furthermore, supply issues for coal tar pitch indicate supply problems will intensify in the upcoming future.
Asphalt based materials are made from distilled petroleum fractions, typically vacuum tower bottoms or perhaps atmospheric tower bottoms. These heavy hydrocarbon fractions are sometimes oxidized or xe2x80x9cblownxe2x80x9d to change the asphalt properties. Asphalt based sealers do not smell as much as the coal tar based materials and are able to withstand a wider range of temperatures. The asphalt sealers are not as toxic and some states permit only asphalt based sealers to be sold. Asphalt sealers do not have the black color desired by many users. Asphalt sealers do not last as long, and frequently must be reapplied every year or every two years.
U.S. Pat. No. 4,222,916, Hergenrother, RUBBERIZED COAL TAR PITCH EMULSION, discloses a coal tar based sealer with acrylate emulsion.
U.S. Pat. No. 4,537,635, Bart et al, discloses a coal tar driveway sealer.
U.S. Pat. No. 4,052,290, Cushman et al, teaches oxidizing or air-blowing of asphalt.
U.S. Pat. No. 4,537,635, Bart et al, teaches driveways sealers from oxidized coal tar.
U.S. Pat. No. 5,558,702, Chatterjee et al, ASPHALT EMULSIONS CONTAINING AMPHOTERIC EMULSIFIER, taught use of asphalt emulsions to xe2x80x9cavoid the use of coal tar and its derivativexe2x80x9d.
U.S. Pat. No. 5,667,576, Chatterjee et al, ASPHALT EMULSIONS, taught forming an asphalt emulsion from AC-20 asphalt and an emulsifier and mixing with varying amounts of a lime/clay/sand/carbon black mixture.
Despite the extensive amount of driveway sealer sold, and an extensive amount of work reported in the patent literature, the work is essentially directed to either a coal tar based material or an asphalt based material. This is probably due in large part to the relative incompatibility of the two types of materials. Although both could be described as heavy, sticky materials, they are vastly different. Asphaltic fractions obtained by distilling crude oil, if heated and poured on your desk, would make a sticky mess that would be difficult to remove. If cooled to room temperature and hit with a hammer, it would dent and coat the hammer head with some asphalt. Pitch with a similar softening point, if heated and poured on a desk, then cooled, would behave differently. It would form a smooth, glassy solid. If hit with a hammer, it would shatter, and could be swept from the desk surface leaving the desk relatively clean.
Some work has been done on blending coal tar and petroleum pitch for a specialty application, anode binder pitch. This work, reviewed next, was directed to blending two pitches (one derived from coal tar, one from petroleum), and did not teach or suggest blending asphalt with a pitch fraction.
U.S. Pat. No. 5,746,906, COAL TAR PITCH BLEND HAVING LOW POLYCYCLIC AROMATIC HYDROCARBON CONTENT AND METHOD OF MAKING THEREOF, was directed to Al anode pitch, for manufacture of anodes for aluminum smelting. The patent taught in this application, that up to 10% asphalt could be blended into coal tar pitch with no ill effect. The use of 60:40 coal tar pitch:petroleum pitch blends was possible by blending a coal tar pitch with a relatively high softening point (130-175xc2x0 C.) with a petroleum pitch with a much lower softening point (75-85xc2x0 C.).
We wanted to make a better asphalt based driveway sealer. We wanted to minimize the amount of expensive, and potentially toxic and foul smelling, coal tar pitch material used. We wanted to maximize use of asphalt, but produce a driveway sealer with better properties than the asphalt based materials previously used.
We discovered that we could make a better asphalt based sealer by using a blend of asphalt and pitch and cut-back oil as a substitute for coal tar pitch. We retained many of the desirable properties of the coal tar based materials, but with reduced amounts of carcinogens. We believe that the cut-back oil acts as a co-solvent for the asphalt and pitch materials, rendering them compatible.
This material retains many of the desirable properties of the coal tar based sealers, but with reduced carcinogen levels due to the reduced amount of coal tar pitch used.
Accordingly, the present invention provides a binder or sealer base comprising pitch, asphalt and cut-back oil.
In another embodiment, the present invention provides driveway sealer emulsion of water, clay and sealer base, wherein said sealer base comprises a blend of petroleum or coal tar pitch with a softening point above 40xc2x0 C., asphalt having a softening point above 40xc2x0 C., and cut-back oil in an amount sufficient to reduce the viscosity of said sealer base to 100 centipoise as measured by rotational Brookfield.
FIG. 1 is a plot of wear resistance of driveway sealer based on percent asphalt in the binder.
FIG. 2 is a graphical presentation of viscosity versus composition for blends of various pitch and asphalt materials.